Color CRT drive apparatus having automatic white balance adjusting circuit and CRT display

ABSTRACT

A picture tube drive apparatus for driving a color picture tube. The picture tube drive apparatus comprises a video output circuit which receives video signals, amplifies them and outputs the amplified video signals, a picture tube drive circuit which receives the video signals amplified by the video output circuit for driving said color picture tube based on video signals, the picture tube drive circuit having a detector for detecting a beam current corresponding to the brightness of each color flowing through the picture tube, a picture tube connected with the picture tube drive circuit for displaying the video signals, a white balance control circuit into which a detection value of a beam current detected by the picture tube drive circuit is inputted and for outputting video signal level compensation signals for adjusting the white balance of the video image displayed on the picture tube to the picture tube drive circuit. A color picture tube in which an electron shield frame having at most a width which will not prevent electron beam from flying onto said shadow mask from an electron gun and having a function to suppress the reflection of the electron beam on a fluorescent screen is disposed on the inner peripheral surface of said electron on the side of the electron gun with respect to a shadow mask mounting position in the color tube.

BACKGROUND OF THE INVENTION

The present invention relates to a drive apparatus for a color cathoderay tube, and in particular to a drive apparatus having an automaticwhite balance adjustment circuit and a color picture tube which iseffective to prevent a reference signal for white balance adjustment asa raster from being displayed thereon.

In a display such as character graphic display, TV receiver or monitorTV receiver which uses a multi-color picture tube a white balanceadjustment is performed by an automatic white balance adjustment circuitas follows. A cut-off adjustment is performed by inputting a whitesignal representative of a relatively dark white to the automatic whitebalance adjustment circuit as a reference signal for white balanceadjustment for adjusting a direct current level of the inputted signalso that the ratio of cathode currents corresponding to current red,green and blue become predetermined ratios. A drive adjustment isperformed by inputting a white signal representative of relatively lightwhite to the white balance adjustment circuit to adjust the gains ofrespective amplifiers so that the ratios of cathode currentscorresponding to current red, green and blue colors become predeterminedratios. The white balance adjustment is thus performed by the automaticwhite balance adjustment circuit so that no color is displayed atvarious areas having various brightness on the screen of the colorpicture tube when white and black video image is reproduced. The presentinvention is concerned with a drive apparatus for a color cathode raytube having a white balance adjustment capability which is obtained byperforming at least the above mentioned cut-off adjustment.

There has heretofore been a problem that a white balance of colorpicture tube which has been adjusted on shipping from a factory isreadily changed after a long term use. This is caused by change withtime due to decrease in electron emission from cathodes and by drift ofcircuits. An automatic white balance adjustment circuit in which changein white balance is recovered is described in, for example, JapaneseUnexamined Patent Publication No. Sho. 60-18087 specification entitled"Color television receiving system".

FIG. 1 is a block diagram showing such a prior art automatic whitebalance adjustment circuit.

In FIG. 1, R (red), G (green) and B (blue) primary color signals whichare inputted to input terminals 1R, 1G and 1B, respectively pass throughsignal synthesizing circuits 8R, 8G and 8B, respectively and areamplified by drive adjustment variable gain amplifier circuits 10R, 10Gand 10B, and then are level-shifted level compensation circuits 11R,11G, and 11B for cut-off adjustment. The signals are amplified to anamplitude which can drive a picture tube 6 by video output circuits 12R,12G and 12B and are supplied to the picture tube 6 through cathodecurrents detection circuits 9R, 9G and 9B.

An automatic white balance control adjustment performed at this timewill be described hereafter with reference to signal waveform at variousparts shown in FIG. 2.

Signals represented at (b) and (c) in FIG. 2 which are extracted from acomposite video signal to be displayed as a video image are applied tovertical and horizontal blanking pulse input terminals 3V and 3H of asignal generation circuit 2 for automatically adjusting white balance,respectively. Two signals 4B for cut-off adjustment and 4W for driveadjustment represented at (d) in FIG. 2 which are generated from thesesignals (b) and (c) are inputted as reference signals for whiteadjustment to the signal synthesizing circuits 8R, 8G and 8B via asignal line 4.

If one (composite video signal) of the inputted three R, G and B primarycolor signals is assumed as (a) in FIG. 2, the output from correspondingsignal synthesizing circuit (8R if 8R) will have a signal wave form as(e) in FIG. 2. If the signal (e) in FIG. 2 corresponds to the primarycolor B signal, a detected voltage which is proportional to a cathodecurrent from a cathode 7B flowing into the emitter of a transistor 28 ina cathode current detection circuit 9B is inputted to a sampling circuit13 via a cathode current detection signal line 30B. Since circuits 9Rand 9G are identical with the circuit 9B in structure, the circuits 9Rand 9G are simply designated as blocks for simplicity of illustration.This is same as the circuits 12R, 12G and 12B.

Gate pulses which are in synchronization with the reference signals 4Band 4W are supplied to the sampling circuits 13R, 13G and 13B via a gatesignal line 5. A negative feedback action by a cut-off adjustmentcomparator (or operational amplifier) 16B and a drive adjustmentcomparator (or operational amplifier) 17B determines an optimumadjustment level in a level compensation circuit 11B for a cut-offadjustment level and an optimum adjustment level in a variable gainamplifier circuit 10B. Control voltages in the sampling circuit 13B atthis time which correspond to the optimum adjustment level of the levelcompensation circuit 11B for cut-off adjustment and the optimumadjustment gain of the gain variable amplifier circuit 10B are held in ahold capacitor 15B for cut-off adjustment and a hold capacitor 14B fordrive adjustment, respectively, and are then supplied as controlvoltages to comparators 17B and 16B, respectively until next samplingtime.

Reference voltage sources 17 and 18 are used for controlling the cathodecurrents on cut-off and drive adjustment to prescribed values,respectively. The above mentioned operation is same in the R and Gprimary color signal circuits.

The reference voltage source 17 is commonly used for comparators 16R,16G and 16B corresponding to three primary colors. The reference voltagesource 18 is commonly used for comparators 17R, 17G and 17B. Thedetected voltage values representative of the cathode currents which areinputted to the inverting terminals (-) of respective comparators viasampling circuits 13R, 13G and 13B are preset at predetermined ratiosnecessary for three primary color signals so that cathode currents forrespective colors can be controlled at ratios necessary to keep thewhite balance. In other words, white balance can be stabilized bycontrolling cathode currents of respective primary colors for thepicture tube on insertion of the reference signals.

SUMMARY OF THE INVENTION

Since level compensation circuits 11R, 11G and 11B are disposed at theprestige of video output circuits 12R, 12G and 12B in the prior artshown in FIG. 1, the signal dynamic ranges after these video outputcircuits should be set at a wide range also in consideration of levelcompensation amount. For example, it is necessary to increase thevoltage of the power source which is to be applied to the terminal 27.Further, in order to assure a resolution which is required for the TVreceiver, lowering in the cut-off frequency of the output circuitdetermined by an output capacitance including stray capacitance ofwiring and a collector resistor 26 should be suppressed. Accordingly, itis not necessary to provide the collector resistor 26 having a highresistance.

Interposing of the cathode current detection circuits 9R, 9G and 9Bbetween the video output circuits and the picture tube increases theoutput capacitance under the influence of parastic capacitance and thelike. Accordingly, it is necessary to lower the value of the collectorresistor 26 for assuring a desired frequency band range.

Therefore, if a voltage applied to the terminal 27 of the power sourceis made constant, power consumption of the video output circuitsincreases since the current flowing through the collector resistor 26increases. In particular, it has been difficult to achieve an automaticwhite balance adjustment for high definition displays which require abroad band range characteristics.

It is an object of the present invention to suppress increase in powerconsumption of video output circuits and to achieve an automatic whitebalance adjustment for display.

In order to achieve the above mentioned object, the present inventionprovides a color picture tube drive apparatus comprising as maincomponents, a video output circuit for amplifying RGB primary colorsignals inputted thereto, a picture tube drive circuit provided on theoutput side of the video output circuit for driving the color picture,said drive circuit having beam current detecting means, and a whitebalance control circuit which receives a beam current detection signaloutputted from the picture tube drive circuit and outputs a video signallevel compensation signal to said picture tube drive circuit so that thecurrent level of the video signal is controlled for adjusting for whitebalance of displayed video image.

Now, the color display which is a TV receiving system or monitor TVadopts an overscan system. That is, one scanning period comprises ablanking interval and a video display interval, and the video displayinterval is made longer so that horizontal video display width slightlyexceeds the width of the screen of the display. As a result, a part ofvideo image is scanned outside of the display screen so that it cannotviewed (disappears). Irrespective of this, the white balance adjustmentreference signal is never displayed on the display screen. Such a systemis an overscan system.

In contrast to this, a character graphic display which is used as, forexample a computer terminal adopts an underscan system.

That is, the video display interval of one scanning period comprisingone blanking interval and one video display interval is preset s thatthe horizontal display width is slightly shorter than that of the screenof the display. The video information to be displayed is prevented frombeing lost as less as possible. On the contrary to this advantage, apart of the white balance adjustment reference signal will be leaked anddisplayed. If the display including the automatic white balanceadjustment circuit described as a prior art adopts the underscan systemof the above mentioned two scan system, there would occur problems asfollows:

(1) If the above mentioned prior art automatic white balance adjustmentcircuit is used in a display adopting the overscan system, the referencesignal for white balance adjustment will not be displayed on the picturetube screen. However, the reference signal is displayed as a raster inthe display adopting the underscan system, resulting in anuncomfortability to users.

(2) The display adopting the underscan system is often used as interfacefor particular computors and the contents to be displayed are alwayssimilar and limited. Accordingly, lowering in luminance efficiency offluorescent material on the screen in particular display positions islarge, resulting in prominent irregular brightness on the screen.

If the above mentioned prior art white balance adjustment circuit isused for the display adopting the overscan system, there would occurproblems as follows:

(3) The deviation of white balance due to change in respective primarycolor fluorescent materials with time cannot be compensated for even ifthe ratios of the cathode currents for respective primary colors arecontrolled to predetermined ratios.

It is an object of the present invention to provide a display includingan automatic white balance adjustment circuit which can solve the abovementioned problems.

(1) In order to solve the problems, an additional deflection signal isapplied from an additional deflection signal generating circuit to asignal path in a deflection circuit of a picture tube via an addingcircuit.

(2) In order to solve the second and third problems, an optical sensoror a video camera is connected with a white balance control circuithaving a white balance compensation data storing circuit incorporatedtherein.

(3) In order to solve the third problems, a count circuit for countingthe operation continuation period of a color TV receiving set to detectchange with time is provided and is connected with a white balancecontrol circuit having a white balance compensation data storing circuitincorporated therein.

(1) The additional deflection signal generating circuit generates asignal representative of a deflection amount to be added to a deflectionsignal of the underscan system. An adding circuit inserted into thesignal path in the deflection circuit adds a signal obtained from theadditional deflection signal to provide a desired deflection signal waveform (waveform which enables the reference signal for white balanceadjustment to be displayed as a raster).

(2) The optical sensor or the video camera serves to measure thedeviation of white balance and provide a data by quantification thereof.The white balance control circuit is capable of drive and cut-offcontrolling so that the brightness irregularity and deviation of thewhite balance are overcome by using the measured data. The white balancecompensation data storing circuit in the white balance control circuitstores a control amount in the above mentioned control and uses thestored control amount to achieve control.

(3) The white balance compensation data storing circuit storespreliminarily given drive and cut-off control amounts of change withtime used for compensation for change in white balance with time. Thecount circuit outputs an address corresponding to the operationcontinuation period (passage time) of the TV system. Based on theaddress, the white balance control circuit reads out the control amountof change with time stored in the white balance compensation datastoring circuit for achieving white balance control.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a prior art;

FIG. 2 is a view showing signal waveforms in various positions in theprior art;

FIG. 3 is a block diagram showing a picture tube drive circuit includingan white balance adjustment circuit which is an embodiment of thepresent invention;

FIG. 4 is a waveform view showing the relation between deflectionsignals of FIG. 3 and the display period;

FIGS. 5A and 5B are views showing the variations of deflection system inthe embodiment in FIG. 3;

FIG. 6 is a view showing the details of a deflection circuit in theembodiment in FIG. 3;

FIG. 7 is a structural view showing a switch circuit of FIG. 6;

FIG. 8 is a partial sectional view showing a main part of a colortelevision receiver;

FIGS. 9A and 9B are a longitudinal sectional view and a front view of apicture showing the structure in FIG. 8, respectively;

FIGS. 10A and 10B are detailed views showing the structure of a gridmount surface in FIG. 8;

FIG. 11 is a structural view showing the details of a white balancecircuit of FIG. 3;

FIGS. 12, 13A and 13B are views showing variations of the embodiment ofFIG. 11;

FIGS. 14A, 14B, 14C;15, 16, 17A and 17B are views showing variations ofthe white balance circuit of FIG. 11 and the operation thereof;

FIGS. 18A, 18B, 19A and 19B are views showing the details of a levelcompensation and cathode current detection circuit in FIG. 3;

FIG. 20 is a view showing a variation of a reference signal insertionadding circuit in FIG. 3;

FIG. 21 is a view showing a variation of reference signal insertioncircuit;

FIG. 22 is a view showing a variation in which a deflection circuit isomitted from the embodiment of FIG. 3;

FIGS. 23 and 24 are views showing another embodiment;

FIGS. 25A, 25B, 25C, 25D and 25E are views showing the structure of afurther embodiment in which automatic white balance adjustment isperformed by detecting the brightness and chromaticity of a colorpicture tube;

FIG. 26 is a view showing the distribution of the brightnessirregularity;

FIG. 27 is a view showing a prior art anode current detection circuit;

FIG. 28 is a view showing a variation of an anode current detectioncircuit;

FIG. 29 is a structural view showing a further embodiment;

FIG. 30 is a view showing an approximate color temperature of areference white color in a color television receiver;

FIGS. 31A and 31B are views showing each primary color cathode currentcharacteristics and normalized cathode current characteristics;

FIGS. 32, 33A, 33B and 34 are structural views showing a furtherembodiment in which the picture tube drive circuit comprising a levelcompensation circuit and a beam current detection circuit;

FIGS. 35 through 39 are structural views showing an embodiment in whichthe picture tube drive circuit comprises a beam current detectioncircuit and a level compensation circuit which are disposed in order;

FIGS. 40 through 43 are structural views showing an embodiment of aclamp circuit suitable for widening the band range of the picture tubedrive circuit;

FIGS. 44 through 48 are structural views showing further embodiment inwhich the picture tube drive circuit comprises a current detection levelcompensation detector;

FIGS. 49 and 50 are views showing the structure of other picture tubedrive circuits; and

FIGS. 51, 52 and 53 are structural view showing embodiments of a beamcurrent detection circuit.

DESCRIPTION OF THE PREFERRED EMBODIMENT

An embodiment of the present invention is shown in FIG. 3.

In FIG. 3, reference numeral 22 denotes a deflection control circuit;31R, 31G and 31B denote level compensation and cathode current detectioncircuits which serve as picture tube drive circuits for driving apicture tube 6. Reference numerals 12R, 12G and 12B denote video outputcircuits; 10R, 10G and 10B denote drive compensation variable gainamplifier circuits; 32R, 32G and 32B denote adding circuits forinserting a reference signal; 33 denotes a white balance controlcircuit.

Respective primary color signals which are inputted to input terminals1R, 1G and 1B from a video signal source such as computer are amplifiedby drive adjustment variable gain amplifier circuits 10R, 10G and 10Band video output circuits 12R, 12G and 12B, respectively and thenapplied to cathodes 7R, 7G and 7B of a picture tube 6 via levelcompensation and cathode current detection circuits 31R, 31G and 31B.

Also in FIG. 3, automatic white balance adjustment is performed byadding reference signals represent as 4B and 4W in 2D which are fed fromthe white balance control circuit 33 via a reference signal line 4 for ablanking period of respective primary color signals so that the ratiosof the cathode current of respective primary colors or cathode currentvalues are constant.

If reference signals are added for a blanking period of primary colorsignals (or only reference signals are inserted independently of primarycolor signals, display of the reference signals is readily avoided amentioned above in the TV receiver which adopts the overscan system.However, if the TV receiver adopts the underscan system as is similar tocharacter graphic display system or peripheral area of an effectivedisplayable screen of the picture tube is used for maintaining thepicture quality such as focus or convergence characteristics, a rasterexisting in a period other than video display period appears in theeffective screen area so that a reference signal for white balanceadjustment may be displayed on the screen.

Hence, in accordance with the present invention, by generating anadditional deflection signal by the deflection control circuit 22 asshown in, for example, FIG. 6, and by supplying it to a deflection coilof a deflection yoke 21, the raster existing for a period other thanvideo display period is shifted from the effective screen area so thatthe reference signal for the white balance adjustment will not bedisplayed.

An example of waveform of the deflection signal which is added with theadditional deflection signal is shown in FIG. 4. In FIG. 4, a solid line43 shows a conventional inherent deflection signal waveform. The lasterfor an initial period of the display period is departed from theeffective screen area by deforming (modulating) the inherent deflectionsignal waveform into that represented by a dot and chain line 44 for theinitial period of the display period. If the TV receiver is of amultiscan type in which many kinds of signals having differentdeflection frequencies are inputted thereto, it is better to limit thedeparting range of the raster by changing of the deflection signalwaveform represented by a dotted line 44 into that represented by adotted line 45.

This aims at suppressing a luminescence phenomenon (halation) of afluorescent material which is otherwise caused reflection, scattering ofthe electrons and secondary electron emission induced by impingement ofelectrons of excessively deflected electron beams on the inner surfaceof a glass bulb, an electrically conductive layer applied thereon andother metal part in the bulb of the picture tube. This phenomenon causesto lower the picture quality that an inherently dark video image can beviewed as a bright image.

If the inherent deflection signal waveform is modulated as representedby dotted lines 44 and 45, a ringing would occur immediately after bentportions in the deflecting signal waveform so that geometricaldistortion will be readily generated in the video image on the screen.In such a case, the ringing in the display period can be eliminated bychanging the time of modulation of the deflection signal waveform to theend of trace period as represented by dotted line 46 or 47 in FIG. 4.

Although an electromagnetic deflecting system using the deflection yoke21 in the deflection device of the picture tube 6 is shown in FIG. 3,the system can overcome the ringing problem by considering thedeflection signal waveform as a deflection voltage waveform rather thanthe deflection current waveform even if the system is an electrostaticdeflection system.

Furthermore, the above description is applied to both horizontal andvertical deflection. It is possible t distribute the deflection signalwaveform shown in FIG. 4 to a plurality of deflection devices(combination of electromagnetic and electrostatic systems in possible)in consideration of performances such as loss in deflection device andsignal dynamic range. This can be achieved by applying values V_(A) andI_(DY) shown in FIG. 5B to an electrostatic deflection electrode 21C3 or21C shown in FIG. 5A and a deflection yoke 21, respectively. At leasteither one of three primary color common electrode 21C and primary colorexclusive electrode 21C may be used as the electrostatic electrode.Accordingly, conventional deflection signal may by inputted to the priorart deflection device and a deflection signal to be added may be addedto an additional deflection device.

An example of a circuit for obtaining a deflection signal waveform inaccordance with the present invention, which has been described withreference to FIG. 4 is illustrated in FIG. 6.

That is, FIG. 6 is a circuit diagram showing in detail as a whole a partcomprising the deflection control circuit 22, the deflection yoke 21,and the deflection circuit in the picture tube 6 with reference to acase of electromagnetic type vertical deflection.

With reference to FIG. 6, conclusion will be firstly described. Adeflection current having a waveform shown in FIG. 4 flows through avertical deflection yoke 21D by a vertical synchronization signalinputted to a terminal 22V and a deflection signal tube to be addedwhich is inputted from a white balance control circuit 33 (FIG. 3) via asignal line 42 or a control signal for additional timing (these signalswill be referred to as deflection control signal).

Now, operation will be described in detail. A sawtooth wave which hasbeen generated by a vertical oscillation circuit 220S passes through anadding circuit 22A1 and thereafter is amplified by a drive circuit 22DRand an output circuit 220 in a vertical amplifier circuit 22AMP and isapplied to a vertical deflection yoke 21D. A deflection current iscontrolled by adjusting the gain of the drive circuit 2DR by a negativefeedback system using a deflection current detection resistor and afeedback circuit 22FB.

That is, the deflection current flowing through the vertical deflectionyoke 21D is detected as a voltage value by a deflection currentdetecting resistor 22R and is fed back to the drive circuit 22DR via afeedback circuit 22FB to lower the amplification gain thereof when thevalue is high. The deflection current is fed back to the drive circuit22DR via the feedback circuit 22FB to increase the amplification gainthereof when the voltage value is low. In such a manner, negativefeedback control is performed so that a given deflection currentconstantly flows through the vertical deflection yoke 21D.

A feature of the circuit shown in FIG. 6 resides in that the deflectionsignal to be added for the above mentioned end is added to the originaldeflection signal by being inserted into a sawtooth wave input line inthe deflection circuit by the adding circuit 22A1 or substantially addedto the original deflection signal by being inserted into the feedbackline by the adding circuit 22A2. This can be accomplished by eitherapproach.

The deflection signal to be added corresponds to, for example, dot andchain lines 44 and 45 and a pair of dot and chain lines 46 and 47 inFIG. 2 can be readily generated by inputting a blanking pulse as atrigger pulse to a circuit similar to the vertical oscillation circuit220S. The resultant deflection signal to be added may be added withoutbeing reversed if the adding circuit 22A1 is used and may be added afterbeing reversed if the adding circuit 22A2 is used.

In order to suppress increase in loss at vertical amplifier circuit 22by application of the present invention, the power voltage source 22V2is added with both or either one of 22V1 and 22V3, which are switched byswitching circuits 22S1 and 22S2, respectively.

This system suppresses power consumption by increasing the power sourcevoltage to be applied only for a period in which the rate of change inthe deflection current is high and by decreasing an average value of thepower source voltage. The switch circuits 22S1 and 22S2 are controlledby an additional deflection circuit 22F or automatically controlled sothat the former 22S1 is turned on only for a retrace or flyback periodor an additional deflection period in which the deflection currentabruptly increases and the latter 22S2 is turned on only for anadditional deflection period in which the deflection current abruptlydecreases. Diodes 22D1 and 22D2 serve as automatic switches which areturned on only when the switch circuits 22S1 and 22S2 are turned off.These functions are realized by a circuit shown in, for example, FIG. 7.

In order to decrease the loss as is similar to the above mentioned powersource switching system, the voltage sources 22V1 and 22V3 of FIG. 6 maybe replaced with high capacity capacitors which ar charged to a voltagesame as the voltage source 22V2 and are switched at a timing similar tothe above mentioned system (this system can be referred to as pumping upand down system).

An exemplary way for a color picture tube effective to prevent thereference signals from being displayed as a raster on the picture tubescreen for some reason even in an overscan system as well as anunderscan system is shown in FIG. 8.

FIG. 8 is a partial sectional view showing a color picture tube. In thedrawing, reference numeral 6G denotes a panel glass; 6K a fluorescentlayer applied on the panel glass; 6S1 a shadow mask frame; 6ES anelectron shield; 6P panel pins used at only upper and lower portions ofthe picture panel. The above structure has heretofore been used.

However, a gap will be formed between the panel glass 6G and theelectron shield 6ES due to a fabrication precision of the panel glass 6Gand the electron shield 6ES and since the electron shield is formed of athin alminium sheet so that it is readily deformed. The gap will bereadily formed at the corners which are complicated shape. This is moreor less same as the upper and lower portions where panel pins 6P areprovided.

Now, an electron beam 6B1 which is deflected to a position justdeparting from the display period will be considered. Since the electronbeam 6B1 is shielded by the electron shield 6ES, it will not be incidentupon the fluorescent layer 6K which is an effective screen, and nohalation will occur which is a fluorescent material luminescence byscattered beam. However, the electron beam 6B2 which is incident uponthe corners of the color picture tube will collide with the inner faceof the panel glass 6E to be scattered. The scattered beam 6B2 is passedthrough a gap between the electron shield 6ES and the panel glass 6G orthe panel pins 6P and then incident upon the fluorescent layer 6K of theeffective screen to cause halation. The impingement of the electron beam6B2 is prevented so that halation due to the electron beam 6B2 will notoccur by providing an electron shield frame having a structure shown inFIG. 8 in such a manner that a shadow mask 6S is omitted from thepicture tube 6 which is shown in longitudinal sectional view of FIG. 9Aand in the front view of FIG. 9B. The electron shield frames 6EF areseparately provided, for example, on the opposite two or four sides ofinner face of the picture tube 6 or integrally formed and disposed. Evenif there is a gap between the electron shield frame 6EF and the panelglass 6G, the electron beam will disappear after repeatingmultiple-reflections.

Mounting of the electron shield frame 6EF on the picture tube 6 isachieved by adapting the panel pins 6P provided in the panel glass 6Ginto adapting recess (not shown) of the electron shield frame 6EF orbonding them, or other suitable means as is similar to mounting of theshadow mask.

In the present invention, emission suppression portions may be coveredwith suppressor grids 6SG1 and 6SG2 in FIGS. 8, 9A and 9B in order tosuppress the secondary electron emission due to impingement of electronbeams on various portions.

The secondary electron emission which will readily occur when theelectron beam impinges on the inside of the color picture tube, inparticular, metal part such as electron shield 6ES and the metallicelectron shield frame 6EF can be suppressed by lowering the spatialpotential in the vicinity of the surface thereof relative to theimpinged surface potential. Therefore, voltage lower than the anodevoltage should be applied to the used suppressor grids 6SG1 and 6SG2.Following two ways are possible to obtain this voltage, for example,

(1) Each of voltage for the focus electrode FE applied to an electrongun or a suppressor grid exclusive voltage is applied to the suppressorgrid 6SG1 or 6SG2 via a pattern formed of the inner electricallyconductive layer of the picture tube as is shown in FIG. 9A.

(2) The suppressor grids 6SG1 and 6SG2 are secured via a material havinga low conductivity, (material which is difficult to cause the secondaryelectron emission) so that a necessary voltage is obtained byself-electrostatic charging due to impingement of the electron beam uponthe grids.

However, heat resistive resin and the like containing fine particles ofcarbon is suitable since there is the possibility that use of securingmaterials having a very low conductivity such as glass cause an innerelectric discharge. Developing this idea, it is possible to apply gridpatterned film of the heat resistive resin upon portions requiringsuppression of secondary electron emission and then reapply theelectrically conductive layer 6CF upon the patterned layer.

If the above-mentioned suppressor grids 6SG1 and 6SG2 are formed of meshof an elastic material, it would be possible to position or mount thegrids in the picture tube 6 by adaption using an elastic force of thegrids.

A structure example of the white balance control circuit 33 as shown inFIG. 3 is shown in FIG. 11. Like components in FIG. 11 are representedby like reference numerals in FIG. 1 showing a prior art.

The structure of the present invention shown in FIG. 11 is largelydifferent from the prior art in that hold capacitors 14R, 14G and 14Bfor drive adjustment and hold capacitors 15R, 15G and 15B for cut-offadjustment are directly connected with control lines 19R, 19G, 19B of avariable gain amplifier circuit and control lines 20R, 20G and 20B of alevel compensation circuit, respectively to provide a high precision andstable circuitry.

For comparison, prior art structure of FIG. 1 will be considered. Sincethe hold capacitors 14R, 14G, 14B, 15R, 15G and 15B are connected withthe inverting inputs of the comparators (or operational amplifiers) 16R,16G, 16B, 17R, 17G and 17B, respectively, sag due to discharge of thehold capacitors is amplified so that this influence is remarkablyincreased to invite instability. Alternatively, necessity to suppressthe gain of an open loop of a negative feedback for avoiding theinstability results in deterioration of precision of the white balancecontrol.

In contrast to this, since increase in amplification degree determinedby a stage from the amplifier circuit to the cathode current detectioncircuit after the stage of each hold capacitor is suppressed in thestructure of the present invention as shown in FIG. 11 so that thesensitivity of each comparator (or operational amplifier) can besufficiently increased, the detection voltage of each cathode currentdetection signal lines 39R, 30G and 30B can be precisely matched to eachvoltage of the reference voltage sources 17 and 18.

The reference signal generation circuit 4P only receives timing pulsesfrom the automatic white balance adjustment signal generation circuit 2.The waveform of the reference signal can be preset or controlledindependently according to respective necessity of the embodiments whichwill be described hereafter.

In FIG. 11, comparators (or operational amplifiers) encircled by dot andchain lines 163 and 173 can be commonly used by ways as follows:

(1) As shown in FIG. 12, the switch circuits 13CR, 13CG and 13CB areshort-circuited with the output terminals of the comparators 13DR, 13DGand 13DB, respectively in the same primary color circuit to form acomparator for each primary color which is commonly used on drive andcut-off adjustments. At this time, the reference voltage sources 17 and28 are switched or alternatively connected with non-inverting input ofthe comparator (or operational amplifier) to supply the same voltage.

(2) In a system in which the balance adjustment is sequentiallyperformed in order of each primary color signal circuit, the circuit maycomprise one comparator (or operational amplifier) for three primarycolors by connecting the terminal of each switch circuit to onecomparator (or operational amplifier) in each primary color circuit. Thestructure of the reference voltage sources 17 and 18 are same as thatset forth in paragraph (1).

The circuit structure and the timing chart of the pulse signals used forswitching each switch circuit set forth in paragraph (2) is shown inFIGS. 13A and 13B.

Since the output of each comparator (or operational amplifier) isshort-circuited to each hold capacitor when the switch circuit is turnedon, the switch circuits can be omitted by forming the comparators (oroperational amplifiers) of current output type and making the outputcurrent zero when the switch is turned off.

However, current output circuits are necessary in lieu of the switchcircuits when the comparators (or operational amplifiers) are commonlyused as mentioned above. Input-output characteristics of the operationalamplifier may be considered same as that of the comparator, both deviceswill be hereafter referred to as comparator.

FIG. 14A is a block diagram showing a further embodiment of the whitebalance control circuit 33 shown in FIG. 3. That is, it shows theembodiment of the white balance control circuit which is stabilized bystoring the control signals of the control lines 19R, 19G and 19B of thevariable gain amplifier circuit and the control lines 20R, 20G and 20Bby using storing circuits in lieu of the hold capacitors.

The digital signal processing circuit 48 shown in FIG. 14A comprises amicrocomputor circuit 51, a memory circuit 52, an interface circuit 50and data busses, an address busses and control busses (among which onlyrepresentative data bus 53, address bus 54, and control bus 55 throughwhich signals flow are shown in the drawing).

In FIG. 14A, a reference numeral 4DA denotes a D/A converter circuit(digital to analog converter circuit) for generating a referencesignals. A control block of an R primary color signal circuit in a framerepresented by a dot and chain line 49R. Similar control blocks of the Gand B primary color signal circuits are commonly represented at 49.

The comparator 16R and A/D converter circuit (analog to digitalconvertor circuit) 15AD are commonly used on both drive and cut-offadjustments in the frame represented by a dot and chain line. Only theswitch circuit 13DR is reversed on drive adjustment so that the outputof the comparator 16R is fed to the digital signal processing circuit 48via an A/D converter circuit 15AD. After it is stored in the memorycircuit 52 according to needs, it is held at the output of the D/Aconverter circuit 14DA and is outputted to a control line 19R byreinverting the switch circuit 13DR which completes the adjustment.

Since use of the circuit configuration shown in FIG. 14A eliminates thenecessity of automatic white balance adjustment in the deflectionperiod, the present invention includes various embodiments as will bedescribed hereafter. The change of the picture tube 6 with time can becompensated for if the output of the D/A converter circuit 17DA isupdated by a cathode current time integrated value, for example, inorder of flow of FIG. 15. A reference voltage value V_(D) (for example,a voltage value of the output of the D/A converter circuit 17DA in thecontrol circuit shown in FIG. 14) is increased by one volt each timewhen a value Y₃₀ corresponding to the cathode current time integratedvalue exceeds a reference value N.

A manual switch 3SW in FIG. 14A will be described in an embodimentdescribed herebelow.

Since negative feedback on white balance adjustment if performed in afast analog circuit (for example, the comparator 16R) and only receivingand holding of each control signals is accomplished by a digital signalsystem in the circuit structure shown in FIG. 14A, speed-up of whitebalance adjustment becomes possible. Since only accepting and holding ofeach control signal is performed in a digital signal system, speed-up ofthe white balance adjustment becomes possible.

However, an output signal from the comparator 16R can be received bydisposing a sample and hold circuit (for example a circuit comprisingthe switch circuit 13R shown in FIG. 14C and a cut-off and driveadjustment hold capacitor 14R) so that data acceptance is stablyperformed by the A/D converter circuit 15AD in the blanking period inwhich the cathode current is not detected and negative feedbackoperation of the analog circuit cannot be performed.

FIG. 16 is a block diagram showing a further embodiment of the whitebalance control circuit 33 which can reduce the number of parts and thecost.

The difference between the circuit structure of FIG. 16 and that of FIG.14 resides in that the A/D converter circuit 15AD and switch circuits13DR and 13CR are omitted and instead of this, an interface circuit 15Idetects the output of the comparator 16R and accepts it as a controldata. Since the output of the comparator 16 is an analog value, itcannot be processed in the digital signal processing circuit 48 withoutconverting it into a digital value. This circuits aims at performing ofthe analog to digital conversion operation without using the exclusiveconverter 15AD of FIG. 14.

If it is assumed that the control data which is an output of thecomparator 16 be an 8 bit digital value, a proper control data can beaccepted by checking the output of the comparator 16R responsive to allcontrol signals at 256 steps (=2⁸ steps) obtained from the D/A convertercircuit 14DA or 15DA and by accepting the control signal from the D/Aconverter circuit 14D or 15DA when the checked output assumes zero.

However, this method takes a maximum 256 step trial period of time,there is the possibility that the adjustment period of time is extended.If an adjustment method which will be described hereafter with referenceto FIGS. 17A and 17B, a proper control data can be accepted by repeatingthe number (the number of bits forming a control data -1) of trials.While the dynamic range for data is divided into half data in thismethod, the range including a desired value is narrowed fast. Detailedmethod will be described with reference to FIGS. 16, 17A and 17B.

The desired value of the control data to be accepted is assumed as01010010.1 by considering a quantization error and increasing theeffective digit number and two registers such as A and B registers areprovided for storing area of the computer 51.

Firstly, an intermediate value 10,000,000 of the dynamic range for datais inputted to the A register which is an input data of the D/Aconverter circuits 14DA and 15DA. The half value 0100000000 is inputtedinto the B register which is an inner operational register. It isdetermined whether the desired value is larger than the A register valuedepending on whether the output of the comparator 16R is negative orpositive when the output of the D/A converter 14DA or 15DA is updated byan A register value. If the result is negative, it is determined thatthe desired value is smaller than the A register value. The B registervalue is subtracted from the A register value. Result is made next Aregister. If positive, it is determined that the desired value is largerthan the A register value. A register value is added with the B registervalue. The result is made next A register value. At this time, the Bregister value is also updated into a half value (practically, it willsuffice to shift the counter value to lower significant bit side once.)

As is apparent from FIG. 17, a control data is accepted to the Aregister by repeating this process (the number of bits forming thecontrol data minus one) times (seven times in the above mentioned case).

In order to perform the white balance adjustment again, the abovementioned accepting process may be repeated by using the current valueas the A register value and a value determined from a maximum driftamount as the B register value.

Details of the level compensation and cathode current detection circuits31R, 31G and 31B in FIG. 3 will be described.

In the prior art shown in FIG. 1, the level compensation circuits 11R,11G and 11B are provided at the prestige of respective video outputcircuits 12R, 12G and 12B. Accordingly, the signal dynamic range afterthese video output circuit should be preset at a wide range inconsideration of the level shift amount. For example, it is necessary toincrease the power source voltage to be applied to the terminal 27 inthe video output circuit. In order to assure a resolution required forthe TV receiver system, lowering of the cut-off frequency of the outputcircuit determined by the output capacitance including stray capacitanceof the wiring and the collector resistor 26 in the video output circuit,should be suppressed so that the resistance of the collector resistor 26cannot be higher.

Therefore, increase in the power consumption of the video output circuitis inevitable. In particular realization of the automatic white balanceadjustment for high definition display and the like which requires awide band range characteristics has been difficult.

In order to solve this problem, the level compensation circuit isdisposed at the postage of the video output circuit and is shown as thelevel compensation and cathode current detection circuit which may bedisposed either before or after the cathode current detection circuit inFIG. 3.

An example of the structure (the structure of the level compensation andcathode current detection circuits 31R, 31G and 31B) is shown in FIG.18A. In FIG. 18A, an electronically controlled voltage source 351Bserving as a level compensation circuit is connected after a videooutput circuit, the band range of which is widened by a parallel peakingof a coil 37L and an emitter peaking of a resistor 41P and a capacitor41C and a cascade connection. The cathode 7B is driven via a cathodecurrent detection and SEPP circuit and a protection resistor 7BR.

Disposing the electronically controlled voltage source 7BR at thepoststage can eliminate a cut-off adjustment margin from the signaldynamic range of the circuit at the stage before the video outputcircuit so that a loss over a wide band range of the video circuit canbe decreased.

An example of the electronically controlled voltage source 351B is shownin FIG. 18B. The voltage level of a constant voltage circuit using atransistor 352T is controlled by using a photo coupler 352C compensatesfor an increase in impedance of the electronically controlled voltagesource 351B at a radio frequency. In order to provide a low impedanceelectronically controlled voltage source 351B, it is necessary to causea sufficient bias current to flow by using a current source 283.

A level compensation and cathode current detection circuit which canwiden the band range is shown in FIG. 19A. In other words, FIG. 19A is acircuit wiring diagram showing another embodiment of the levelcompensation and cathode current detection circuit in FIG. 3.

In the circuit shown in FIG. 19A, a cathode current detection circuit isdisposed at the prestige of the level shift circuit so that a highfrequency element having a low voltage resistance can be used as atransistor for an SEPP circuit. Application of bias voltage between twobases of two transistors forming the SEPP circuit improves the highfrequency characteristics.

In the circuit shown in FIG. 19A, the cathode current is detected by theSEPP circuit to perform a level compensation by a clamp circuitcomprising a coupling capacitor 352B and a switch circuit 353B and thecathode 7B of the picture tube 6 is driven via a serial peaking coil7BL.

Specifically, when the switch circuit 353 is turned on to be closed, theoutput of the coupling capacitor 352B is clamped by a voltage appliedfrom a white balance control circuit 33 to achieve a level compensation.When the switch circuit 35 is turned off to be opened, a small cathodecurrent of the picture tube 6 gradually flows into the couplingcapacitor 352B to cause a change in level during opening of the switchcircuit. The switch circuit 358B is turned on at least once every periodin which the change in level falls within the change in level which canbe deemed as constant (for example, horizontal scanning period).Practically, the switch circuit 353B comprises a diode, which isrendered conductive for blanking period by using the increase in thecathode voltage of the picture tube for blanking and is renderedinconductive by using decrease in cathode voltage in a video displayperiod. Alternatively, the switch circuit 353B comprising an activeelement such as transistor is rendered conductive for a period in whicha cut-off searching signal is inputted to the input 40B of the videooutput circuit. However, in this case, blanking is performed by applyinga blanking signal to electrodes (for example a first grid) other thanthe cathode of the picture tube 6.

The switch circuit 353B in FIG. 19A can be realized, for example, in amanner shown in FIG. 19A. The switch circuit 353B is realized by turningon or off the transistor 353Q in FIG. 19B. At this time, a forward basecurrent I_(B) which flows through a base resistor 353R1 when thetransistor 353Q is turned on is restricted and the switching speed iscontrolled by presetting a base by-pass current I_(B) flowing through aresistor 353R2 when the transistor 353Q is turned on. The influence ofthe cut-off control voltage (emitter voltage of the transistor 353Q) tothe switching characteristics of the transistor 353Q is eliminated bythe action of the coupling capacitor 353CB.

It is needless to say that a clamp voltage applied to the switch circuit353B from the white balance control circuit 33 is a voltage which isgenerated by a negative feedback circuit so that the detected cathodecurrents 20B, 20G and 20R in the picture tube 6 is a constant. It isalso apparent that the coupling capacitor 352B is inserted in a signalpath leading to the cathode of the picture tube 6 to couple the signalto cathode.

Since the above mentioned SEPP circuit is provided at a prestige of thelevel compensation circuit, the transistor 28 forming the SEPP circuitmay include an element which is excellent in frequency characteristicsrather than voltage resistance. The above mentioned transfer insensitiveband of the SEPP circuit can be eliminated and the deterioration offrequency characteristics can be compensated for by inserting the switchcircuit 281S which is controlled so that it is turned on only ondetection of the cathode current.

A main part of the display including an automatic white balanceadjustment circuit which is a further embodiment of the presentinvention is shown in FIG. 20.

If the automatic white balance adjustment is performed in a TV receiversuch as high definition display using a wide band range signals, radiofrequency cross-talk is increased due to increase in the number ofsignal leakage paths, in particular, among the primary color signalcircuits. In the embodiment of the present invention as shown in FIG. 3,in order to avoid cross-talk via the reference signal line 4 commonlyused by the primary color signal circuits, three reference signalgeneration circuits 4P are independently used to output an exclusivesignals for each primary color signal circuit. In the embodiment shownin FIG. 20, suppression of the cross-talk is achieved by suppressingincrease in the circuit scale.

In FIG. 20, reference signals are inserted from the reference signalline 4 by using signal switching circuits 32RS, 32GS and 32BS in lieu ofthe reference signal insertion adding circuits (32R, 32G and 2B in FIG.3). It will suffice to cause pulse signals for reversing the positionsof the switches 32RS, 32GS and 32BS from the illustrated position toflow through the line 32S for controlling the switch circuits 32RS, 32GSand 32BS, at least for timing periods 4B and 4W for cut-off and driveadjustments shown in FIG. 2D.

Control of turning on or off of these switches may be simultaneously orsequentially conducted in each primary color signal circuit.

Possible signal leakage paths can be considered to be only capacitors1R4C, 1G4C and 1B4C representing parastic capacitance between switchcircuit terminals and the signal lines (the switch circuit control line32S can easily suppress the signal leakage since it is for transmittinglogical signals).

It is of course that the present invention can be applied to prior artoverscan system which does not require the above mentioned deflection.

Another system for inserting reference signals in consideration ofcross-talk among the primary color signal circuits is shown in FIG. 21.

In FIG. 21, primary color signal inputted from the terminals 1R, 1G and1B are subjected to contrast control by amplifiers 57R, 57G and 57B andbrightness control by adding circuits 56R, 56G and 56B or 58R, 58G and58B and thereafter subjected to automatic control of drive adjustment bygain variable amplifier circuits 10R, 10G and 10B. Variable resistors61V and 62V are provided for brightness and contrast adjustment.

Generation of the cross-talk is sufficiently suppressed since the directcurrent level added to each primary color signal by the bright controlis transmitted through the sample and hold circuit comprising a holdcapacitor or a digital memory circuit.

The brightness control is performed by applying a direct currentregeneration at timing of clamp pulses generated from synchronizationpulses so that each primary color signal is at the same level as thebright control voltage and by maintaining the direct current additionlevel at this time by the sample and hold circuit for a display period.

Accordingly, if the primary signal color circuits comprise integratedcircuits so that they are sufficiently matched with each other,brightness control could be possible even if the d.c. voltage of thebrightness control terminal 61 (or d.c. voltage corresponding to thisvoltage) is added via the sample and hold circuits 60R, 60G and 60B byomitting the comparators 59R, 59G and 59B. Alternatively, the comparatormay be connected with only one primary color signal circuit to apply thebrightness control signal to the input terminal of the comparator. Inthe latter case, the output of the sample and hold circuit at the poststage thereof is commonly used in each primary color circuit and isadded to each primary color signal.

Also in FIG. 21, the switch 63 is reversed at least at the timing of thepulses 4B and 4W as is similar to embodiment of FIG. 20.

Although a prior art brightness control system has been described withreference to FIG. 21, the reference signals for automatic white balanceadjustment are inserted into each primary color signal by using thebrightness control circuit in accordance with the present invention.

Accordingly, the reference signal issued as a brightness control voltageby the switch circuit 63 on the automatic white balance adjustment asshown in FIG. 21. Brightness adjustment in the direct coupling typevideo circuit comprising ICs is stabilized by negative feedback to theoutput thereof. Therefore, the present embodiment is suitable to performthe automatic white balance adjustment by using a multi-purpose videoprocessing IC. It is of course that the present embodiment is applicableto an overscan type TV receiver which does not require the abovementioned additional scanning.

An embodiment of the present invention which make it possible toautomatically adjust while balance of the underscan system TV receiverwithout using the above mentioned additional deflecting means is shownin FIG. 22. The embodiment of FIG. 22 is different from that of FIG. 3in that the deflection control circuit 22 is omitted from the latter.The automatic white balance adjustment reference signal is controlled sothat it is not prominent to give no uncomfortability to users althoughit is displayed on the picture tube.

Ways of control are exemplarily listed as follows:

(1) The automatic white balance adjustment is not performed in avertical deflection period (or horizontal deflection period) asrepresented by reference signals 4B and 4W having waveforms of FIG. 2D,but in so long period that no uncomfortability is given to users (forexample, two signal having a level as low as 4B are inserted in a perioduntil the display period of a video signal). If it is necessary toconduct the automatic white balance adjustment for a so long period thatit cannot be stably performed by the white balance control circuit 33using the hold capacitors shown in FIG. 11, the white balance controlcircuit 33 using memory circuits shown in FIGS. 14 and 16 should beused.

(2) No uncomfortability is given to users by dispersing the displayposition of the automatic white balance adjustment reference signals(particularly white level reference signals for drive adjustment) on theeffective screen of the picture tube. For example, the interval of thewhite level of the reference signal is shortened only in a very shortperiod of the horizontal scanning line or scanning line used for displayof the reference signal is periodically changed.

(3) A combination of methods set forth in (1) and (2) are used. It is ofcourse that signal switching circuits or brightness control circuits maybe used to insert reference signals as well as using adding circuits32R, 32G and 32B, respectively.

An embodiment is shown in FIG. 23 in which users throw an automaticwhite balance adjustment switch according to needs and allow theadjustment reference signals to be displayed on the effective screen ofthe picture tube.

In FIG. 23, a white balance control circuit 33 is added with anautomatic white balance adjustment switch 3SW. The automatic whitebalance adjustment is performed only when the switch 3SW is turned on.Thereafter the control signal obtained at this time each control lines19R, 19G, 19B and 20R, 20G and 20B are maintained.

Accordingly, it is more advantageous to use the memory circuit system asshown in FIGS. 14 and 16 as the white balance control circuit 33. Ifadjustment pattern for deflection circuit system and convergence circuitsystem are displayed by using the white balance control circuit 33 whichoutputs a reference signal responsive to the switch 3SW, variousadjustments could be effectively performed to provide a TV receiverhaving an adjusting signal source therein.

It is of course that adding circuits or brightness control circuits maybe used to insert the reference signals as is similar to the embodimentsshown in FIGS. 21 and 22.

An embodiment of the automatic white balance adjustment circuit in whichit is not necessary to generate reference signals for the automaticwhite adjustment, so that it can be used for both underscan and overscansystems is shown in FIG. 24.

In FIG. 24, the ratios of the input signal level of primary colorsignals (including brightness levels) are control to make the detectedlevels of the cathode currents for primary color signals equal.Alternatively, the input signal levels may be controlled to provide apredetermined relation between the input signal level and the cathodecurrent detection level, rather than the ratio. For example, the inputsignal levels are controlled so that a value which is obtained bymultiplying the input signal levels with γ (γ is a γ compensationconstant of a video signal system) is proportional to the cathodecurrent level.

For example, any one of an average value, a peak value, or minimum valueof the primary color signal inputted to an input terminal 1R or amomentary value at a constant timing (for example, a front porch of orback porch of a horizontal synchronization pulse at which the videosignal is at the black level) is detected by a input signal detectioncircuit 64R. An average value, a peak value, a minimum value or amomentary value of the cathode current is similarly detected by thecathode current level detection circuit 66R.

A gate circuit which open only for a display period or a part of frontor back porch of the synchronization pulse may be in series connectedwith the input terminal of each detection circuit 64R, 64G, 64B and 66R,66G and 66B. The output of the gate circuit on cut-off (low brightnesswhite balance) adjustment and drive adjustment is fed to the whitebalance control circuit 33 via a dividing output line or two systemoutput line when it is synchronized with the adjustment.

For example, cut-off (low brightness level white balance) adjustment isperformed by using a momentary value of the inputted primary colorsignal and cathode current detection signals at one part of the front orback porch of the synchronization signal or a minimum value for adisplay period. Cut-off (low brightness level white balance) adjustmentshould be performed by changing the cathode current detection leveldepending upon the brightness control or by inserting a reference signalwhich is not related to the brightness control into a part (immediatelybefore and after of a blanking pulse in which the primary color signalis not subjected to blanking) of a blanking period. The drive adjustmentis performed by using a peak value or an average value in the inputtedprimary color signal and the cathode current detection signal (a peakvalue or an average value for a display period is possible).

However, a limiter function for a maximum value control in considerationof the signal dynamic range and a minimum value compensation or a noiselimiter function in consideration of malfunction due to noises may beadded on detection of the peak value or the average value.

An embodiment of the present invention which can compensate forirregularity of brightness and chromaticity of the color picture tubeand the changes thereof with age is shown in FIG. 25A.

The color picture tube generally has a brightness irregularity due todifferences in application condition of a fluorescent material or wallthickness of the front glass, which is difficult to be removed in amanufacturing process. An example of the distribution of brightnessirregularity is illustrated by solid lines in FIG. 26. The brightnessirregularity may be promoted in a TV receiver using a deflection andhigh voltage integrated circuit since parabola modulation applied to thehorizontal deflection current for compensation for pincushion distortioncannot be removed from a horizontal flyback pulse.

Since the sage frequency is higher at the upper and left area of theeffective screen of the picture tube such as character display, thebrightness irregularity distribution changes with age as represented bya dotted line in FIG. 26.

The change with age is different among the primary color fluorescentmaterials. Chromaticity irregularity will occur. The irregularities ofbrightness and chromaticity and changes thereof with time can also beeliminated in accordance with the embodiment of the present invention.

In FIG. 25A, it is possible to omit cathode current detection signallines 30R, 30G and 30B to detect no cathode current. Instead of this, itis necessary to connect an optical sensor 68 or a video camera 69 andthe like with a white balance control circuit 33 for directly detectingthe luminance brightness of the fluorescent material.

The automatic white balance adjustment is conducted as follows:

A small window pattern comprising upper and lower divided areas of brownand white are displayed in the center or peripheral area (not shown) ofthe effective screen as shown in FIG. 25B. Cut-off adjustment of darkbrightness is performed based on the dark area in the pattern and thendrive adjustment of light brightness is performed based on the whitearea. Alternatively, adjustment may be conducted by alternatelydisplaying brown and white pattern in one window.

Alternatively, a test pattern which is also used for deflection systempattern is displayed. Brightness and chromaticity at various areas aredetected by the optical sensor 68 or the video camera 69 which isdisposed on the rear side of the screen if the receiver is of projectortype TV receiver type so that users cannot notice the presence of thesensor or the camera to perform the automatic white balance adjustmentfor eliminating the irregularity.

For example, adjustment is performed by a method shown in flow chart ofFIG. 25D. The automatic white balance adjustment can be performed bycontrolling the total luminance characteristics of the entire of the TVreceiver including the luminance characteristics of the fluorescentmaterial of the picture tube by using the structure shown in FIG. 25A. Agreat advantage of using the structure shown in FIG. 25A resides in thatluminance or brightness irregularity (possible for black and white ormono-color display picture tube such as projector tube) or chromaticityirregularity can be compensated for. Specifically, as is shown by a flowchart of a process flow of FIG. 25D, balance adjustment positioning iscarried out on every spot on the screen and the signal value detected bya sensor in this position is inputted. Test standard values which willbe reference values are preliminarily preset in the above mentionedstore means provided in the white balance control circuit 33. Thedetected signal of the sensor is compared with one of the referencevalues. If they do not agree, drive adjustment and cut-off adjustment ofa given amount are conducted and the detected signal is compared with areference value again. As a result if the detected value agree with thereference value, an adjustment value at this time is stored as anadjustment data and the adjustment at this adjustment point iscompleted. The above mentioned operation is sequentially repeated atevery adjustment point to conduct white balance adjustment.

Specifically, the light from the screen on which brightness andchromaticity is irregular in different positions is detected by theoptical sensor 68 or the video camera 69. The gain adjustment of thegain variable amplifier circuits 10R, 10G and 10B and the levelcompensation of the level compensation circuits 31R, 31G and 31B iscarried out by the white balance control circuit 33 so that the detectedlight amount is constant irrespective of the position on the screen.Irregularity of brightness or chromaticity on the screen can thus beeliminated. The summary of this operation is shown in FIG. 25D.

On the other hand, white balance control data are consecutively read outfrom the white balance control circuit 33 according to scanning onnormal video display. If the optical sensor 68 is incorporated in thescreen or the white balance detection is always possible by the use ofthe video camera 69 at this time, necessity of detection of the cathodecurrent is eliminated.

If the optical sensor or the video camera and the like cannot always beused for detecting the white balance, the cathode current afterdetection and adjustment of brightness and chromaticity is detected andcontrol is usually achieved based on the detected cathode current.

Use of video camera 69 and the like makes it possible to perform a fullautomatic adjustment since taking a picture of the entire screen of thepicture tube makes it possible to detect the display position.Furthermore, the signal lines are reduced to two lines for brightnessand chrominance signals and the primary color signal may be reproducedthereafter. There is provided a memory circuit 52 shown in FIGS. 14 and16 in the white balance control circuit 33, in which a control mapstoring the display positions and the white balance control signals arestored is formed. The white balance control data are consecutively readout from the circuit 52 depending upon the timing of the blanking pulseetc. or the amount of the deflection current to eliminate the brightnessand chromaticity irregularity.

If white balance detection is always possible by the optical sensor 68and the video camera 69, or the white balance adjustment is performed bydetecting the cathode current, brightness and chromaticity irregularityof the color picture tube and change of the TV receiver with age can beeliminated by preliminarily storing brightness and chromaticityirregularity compensation data or compensation data for change with agebased on the cathode current are stored in the white balance controlcircuit 33 (change with time can be detected by counting the clocks orvertical synchronization pulses, or by using an integrated value of thecathode current of the picture tube as shown in FIG. 15).

In addition to the above description, compensation data showing how muchcathode current can eliminate brightness and chromaticity irregularityon the screen and compensation data on change with time (compensationdata showing how much the cathode current should be changed tocompensate for brightness or chromaticity irregularity to eliminate itsince how much brightness and chromaticity irregularity is predictedafter passage of predetermined ages can be preliminarily determined bymanufacturer's tests and experiments. Accordingly, brightness andchromaticity irregularity on the screen can be eliminated without usingthe optical sensor 68 or the video camera 69 if these data are stored ina memory circuit.

Another great advantage of detecting the brightness and the chromaticityon the tube screen by the optical sensor 68 or the video camera 69 asshown in FIG. 25A resides in that variations of total luminancecharacteristics and change with time of products including fluorescentmaterial of picture tubes can also be compensated for. Further, sincereduction in circuit scale can be achieved by omitting the beam currentdetection function from the above mentioned picture tube drivingcircuit, a high power and wide band video circuit can be provided byreducing the additional capacitance to the video signal path in thecircuit. Further, it is of course that an adding circuit and brightnesscontrol circuit may be used for insertion of the reference signal as issimilar to FIGS. 21 and 22.

An embodiment of the present invention which is devised to prevent theprimary signal circuit from deteriorating its frequency band rangecharacteristics will be described.

Since the above mentioned automatic white balance adjustment circuit isadded with the cathode current detection circuit as shown in FIGS. 18Aand 19A, the output capacity is increased s that the frequency bandrange of the video output circuit is narrowed.

In order to solve the problem, the cathode current detection circuit isomitted and the beam current for each primary color is detected from theanode current of the picture tube in the present embodiment.

Prior art detection of picture tube anode current is carried out by apart of an automatic brightness limitation (ABL) circuit as shown inFIG. 27.

In FIG. 27, a reference numeral 74 denotes a flyback transformer; 76 ahigh voltage detection terminal; 70 an ABL terminal.

However, a detected current 79 includes a current 80 flowing through ahigh voltage detection breeder resistors 77 and 78 as well as an anodecurrent 81. A time constant of an anode current detection resistor 72and a stabilization capacitor 71 is very high to stabilize the action ofthe automatic brightness limitation circuit so that a peak value of thecurrent cannot be detected.

Hence, in accordance with the present invention, the peak value of thecurrent 79 is detected by inserting a stabilization resistor 83 whichcan be considered as a sufficiently high resistor in comparison with theanode current detection resistor 72 as shown in FIG. 28 illustrating amain part of a further embodiment of the present invention. Since thecurrent 80 can be considered to be substantially constant, the anodecurrent 81 is detected from the change in the current 71 caused when asignal voltage is applied to the cathode of the picture tube 69.

In practice, the anode current 81 is detected by inserting referencesignals to each primary color signal circuit. Although the anode current81 includes a current component flowing through the other electrode suchas a second grid and a distortion current component such as high orderdistortion current of the deflection period flowing across the groundand each wiring of a flyback transformer and flowing through a parasticcapacitance between ABL terminal wirings, the currents other than thebeam current can be considered to be substantially constant inamplitude. Accordingly, the beam current for each color can be detectedby detecting the changes in the peak value, the average value of thecurrent 79 and the momentary value on sampling the present invention isnot only applicable to the underscan system, but also applicable to theunderscan system.

A main part of the embodiment of the present invention in which colortemperature adjustment for a reference white color can be easilyperformed by white balance adjustment is shown in FIG. 29 and will nowbe described.

A summary CIE chromaticity diagram of white color is shown in FIG. 30.Reference numerals 87R, 87G and 87B denote luminance chromaticitycoordinates of each primary color fluorescent material of a picture tubein FIG. 30. Points 84 and 85 denote chromaticity coordinates of(9300K+27 M.P.C.D) and (6550K+7 M.P.C.D) used for reference white color,respectively. Since the chromaticity tracing when the color temperatureof a reference white color is changed passes through points 84 and 85and changes along a black body tracing 86, it can be considered to besubstantially rectilinear.

For example, the relation between the reference white color temperatureand the cathode current of each primary color under a constantbrightness in a picture tube is shown in FIG. 31A.

The color temperatures represented at 91 and 92 show 6500K and 9300K,respectively.

Since cathode current characteristics of each primary color 88, 89 and90 shown in FIG. 31A can be deemed to be substantially rectilinear in anapplicable range, the user can adjust the color temperature of whitecolor by replacing a variable resistor type circuit of FIG. 29 with anautomatic white balance adjustment circuit used for a cathode currentdetection circuit.

In FIG. 29, variable resistors 292R, 292G and 292B comprise a rotaryangle triple serially controlled type element. The relation between thecolor temperature of reference white color and the normalized cathodecurrent for each primary color while one of primary color cathodecurrents is constant is shown in FIG. 31B.

Although at least two elements are enough to form the above mentionedvariable resistor, reliability of the variable resistor can be enhancedby selecting one primary color which makes the cathode current detectionresistor constant. This is due to a fact that if the current is allowedto flow from a slider of the variable resistor for a long period oftime, carbon resistor material around slider contacts would be removedby a galvanic corrosion phenomenon so that inferior contact anddiscontinuities occur in a resistance variable range.

Therefore, occurrence of the galvanic corrosion can be avoided byselecting one primary color which makes the cathode detection resistorconstant and by changing the resistances of the variable resistors ofthe other two primary color in the same direction.

To a picture tube having a characteristics as specifiedly shown in FIGS.31A and 31B, the resistance of an R or B primary color cathode currentdetection resistor is made constant and the other two primary colorcathode current detection resistors are formed by connecting variableresistors 292G and 292B as shown in FIG. 29.

Similarly, the color temperature may also be made variable by making oneof drive control or cut-off control variable and by tracking the othercontrol by the automatic white balance adjustment.

If it is necessary to perform cut-off and drive adjustment under aconstant picture tube brightness when the color temperature is changed,these adjustments may be performed by a method as follows: Thebrightness on respective adjustments can be made constant by changing areference signal or comparison reference voltage generated from thewhite balance control circuit (for example, a reference signal outputtedto the reference signal line 4 and a reference voltage outputted from aD-A converter circuit 17D to a non-inverting terminal of the comparator16R).

Alternatively, it is possible to store various data of the beam currentsor luminance brightness ratios of each primary color in the whitebalance control circuit 33 incorporated in the memory circuit 52 shownin FIGS. 14 and 16, and to use them by user's selection.

At this time, it is possible to perform the automatic white balanceadjustment to provide a reference white color of desired colortemperature by operation such a linear approximation from stored pluraldata. It is of course possible to perform the compensation for thescanning position and change with age on presetting the temperaturecolor.

The present invention can be applied as variations as follows: Thecathode current detection resistors of picture tubes of various color TVreceivers are replaced with electronically controlled resistors and theoptical sensor or a combination of the optical sensor and the automaticwhite balance adjustment apparatus are commonly used for various TVreceivers to perform adjustments. Alternatively, reference data forwhite balance adjustment stored in various color TV receivers andsystems are made controllable from outside and the optical sensor or acombination of the optical sensor and the automatic white balanceadjustment apparatus are commonly used for various TV receivers toperform adjustments. Comparison of performance of various receiver orcolor design simulation can be performed by using cathode currentdetection resistor values relevant to each TV receiver or usingreference data for white balance adjustment controlled from outside.

Now, an embodiment, the block diagram of which is shown in FIG. 32 inwhich a picture tube drive circuit 911 provided between the videocircuit 12 and the picture tube 6 comprises a level compensation circuit11 and the beam current detection circuit 9 will be described withreference to circuit diagrams of FIGS. 33A, 33B and 34. Although only aprocessing circuit of R signal component will be described andillustrated hereafter, it is of course that same processing of G and Bsignals are performed in the other circuits. Description andillustration of components of circuits other than the video outputcircuit 12, picture tube drive circuit 911 and the picture tube 6 areomitted, since they are identical with those of the embodiment shown inFIG. 3.

In FIG. 32, a reference numeral 131 denotes an input signal source, 12 avideo output circuit, 11 a level compensation circuit, 9 a beam currentdetection circuit, 6 a picture tube. In FIG. 32, the picture tube drivecircuit 911 comprising the level compensation circuit 11 and the beamcurrent detection circuit 9 disposed at the poststage thereof isdisposed at the poststage of the video output circuit 12. Powerconsumption of the video output circuit 12 can be reduced by using astructure shown in FIG. 32. Detailed circuit structure of the embodimentof the present invention, the block diagram of which is shown in FIG. 32is shown in FIG. 33A. In FIG. 33A, reduction in power consumption of thevideo output circuit is achieved by inserting a level compensationcircuit 110 which is controlled by a signal transmitted from a controlline 20R between the video output circuit 12 and the picture tube 6. Theband range of the video output circuit 12 is widened by a cascadeconnection of the transistors 24 and 241, an emitter peaking of acapacitor 252 and a parallel peaking of a coil 261. A resistor 25presets the gain of an emitter grounded amplifier circuit comprising thetransistor 24, and a resistor 251 presets the characteristics of theemitter peaking. A reference numeral 27 denotes a voltage sourceterminal of the video output circuit. A terminal 242 is for applying abias voltage to the base of the transistor 241 forming the base groundedamplifier circuit. The level shift amount of the level compensationcircuit 110 is controlled by the signal transmitted from the controlline 20R. The beam current detection circuit leads the cathode currentflowing through the emitter of the transistor 28 to convert the currentinto a voltage signal by a detection resistor 29 to output it to asignal line 30R. At this time, the cathode current includes a leakcurrent from the other electrodes in the picture tube in addition to thebeam current. Therefore, in order to detect the beam current, thedetected beam current is made sufficiently higher than the leak currentor the leak current is cancelled by means which will be describedhereafter.

A diode 282 and a resistor 284 are adapted to protect the transistor 28when a discharge occurs in the picture tube. γ-compensation can beachieved by adjusting the value of the resistor 284.

Deterioration of frequency characteristics of the drive circuit iscaused by a stray capacitance 71R of the picture tube, a straycapacitance 293 of a signal adjusting the value of the resistor 284.

Deterioration of frequency characteristics of the drive circuit iscaused by a stray capacitance 71R of the picture tube, a straycapacitance 293 of a signal line 30R connected with a parasticcapacitance 281 of the transistor 28 and a parastic capacitance of adiode 292 when a resistor 291 is zero ohm.

Hence, in the present embodiment, the value of the resistor 291 shown inFIG. 33A is preset sufficiently higher than the value of a resistor 26,or a parallel impedance of the stray capacitance 293 and the parasticcapacitance of the diode 292 at a frequency at which the above mentioneddeterioration of the characteristics becomes a problem. This caneliminate an adverse effect of the stray capacitance caused via theparastic capacitance 281 of the transistor 28. The capacitor 283 servesto bypass a video signal for compensating for the insufficient picturetube drive ability of the transistor 28 at high frequencies. This bypassaction eliminates a mirror effect due to amplifying action of thetransistor 28. The diode or Zener diode 292 has functions to protect acontrol circuit connected via the signal line 30R, to enhance the beamcurrent detection sensitivity by the increase in the value of theresistor 29 and to suppress the saturation of the transistor 28 due toincrease in collector voltage. It is of course that the transistor 28may be connected with other active elements such as FETs, vacuum tubesand the circuit including passive elements shown in FIG. 33A. In thiscase, it is of course that impedance 291A, 291B which function similarlywith the resistor 291 in FIG. 33A are necessary.

A modification of the embodiment of FIG. 33A is shown in FIG. 33B. Thismodification is substantially identical with the embodiment of FIG. 33Aexcept for the structure of the beam current detection circuit 9 in FIG.33A. The beam current detection circuit 9 shown in FIG. 33B includes avideo signal bypass capacitor 283 which is in parallel connected withvideo signal transmission diodes 282 and 282B, a video signaltransmission resistor 282A having a high resistance value to restrictthe detection leakage of the cathode current. The video signal outputline connected with the picture tube 6 is grounded via a frequencycharacteristic compensation impedance 291B and a spark gap element 284for protecting the circuit against discharge in the picture tube. Asignal on the video signal output line to the picture tube 6 isvoltage-divided by a frequency characteristics compensation impedance291A and a resistor 29 to be outputted to the signal line 30R.

An embodiment which is effective to increase the amplitude of the drivevoltage and the beam current or drive in association with big and highbrightness picture tube is shown in FIG. 34. When the drive voltage andcurrent on drive is increased, the transistor 28 is saturated by a factthat the voltage across the emitter and the collector is decreased sothat there is the possibility that the drive action of the picture tubeand the detection of the beam current will be discontinued. In FIG. 34,the voltage across the base and collector of the transistor 28 isprevented from being forwardly and largely biased by a clamp action ofthe transistors 285 and 286. The type of the transistors 285 and 286 maybe desiredly selected provided that they meet the absolute ratingrequirements such as resistive reverse voltage. The diodes may beSchottky barrier diodes in view of fast response or both diodes may bedifferent in type. For example, enhancement of saturation preventioneffect is made possible by a Baker clamp type using by forming thediodes 285 and 286 of silicon and germanium diodes, respectively.

An embodiment in which a picture tube drive circuit is provided at thepoststage of the video output circuit and the picture tube drive circuitcomprises a video detection circuit and a level compensation circuitwhich are provided at the prestage and the poststage, respectively isshown in a block diagram of FIG. 35. Power consumption of the videooutput circuit 12 may be suppressed and the band range of the beamcurrent detection circuit 9 may be widened by using a structure shown inFIG. 35. Detailed circuits in the block diagram of one embodiment of thepresent invention shown in FIG. 35 is shown in FIG. 36.

A high performance element having a low resistive reverse voltage can beselected as the transistor 28 used in the beam current detection circuitby forming the circuit as shown in FIG. 36. For example, an elementhaving not higher than 70 V may be used although the element having notless than 160 V should be used in the embodiment of FIG. 4. Generally,the amplification ability and excellence in high frequencycharacteristics and low parastic capacitance of the active element isconsistent with the resistive reverse voltage. For example, thedetection precision of the beam current can be enhanced and the minimumdetection current can be reduced by selecting an element having a highamplification as the transistor 28. That is, I_(cbo) can be reduced. Thefrequency band range of the drive circuit can be widened by improvingthe high frequency characteristics of the transistor 28 or by reducingthe parasitic capacitance. If the reliability of the level compensationcircuit 110 can be assured, the protection resistor 284 shown in FIG. 36could be moved to a position between the beam current detection circuitand the level compensation circuit or could be omitted. It is preferableto dispose the protection resistor 48 immediately before the picturetube as shown in FIG. 36 in consideration of protection of the levelcompensation circuit 110 and the deterioration of the frequencycharacteristics by the parastic capacitance of the protection circuit.

An embodiment in which the level compensation circuit 110 of FIG. 36includes a clamp circuit is shown in FIG. 37. In the circuit shown inFIG. 37, a level controlled clamping voltage source 116 is connectedwith the base of a clamp transistor 113 via a clamp switch 115 to clampa coupling capacitor 111 on the side of the picture tube. Change inclamp level (black fall) due to leakage of a discharge current toperipheral circuit is eliminated by making a discharge current flowingthrough the coupling capacitor 111 a circulating current across theemitter and collector of the transistor 113. In case of FIG. 37, theblack fall caused by addition of a sum of the forward voltage due toconduction of the diode 282 and the forward voltage across the base andthe emitter of the transistor 28 to fall of voltage across the resistor26. A resistor 118 serves to increase the base voltage of the transistor113 to a power source voltage connected with the terminal 117 in anon-clamping period in which the switch 115 is opened. Accordingly, areverse voltage is applied to a diode 112 in a non-clamping period sothat the emitter of the transistor 113 is released from the couplingcapacitor 111. A diode 114 is a protection diode for assuring a reversevoltage condition across the base and emitter of the transistor 113 in anon-clamping period and on discharge of the picture tube. The clampcircuit shown in FIG. 37 synchronous with the turning on or off of theclamp switch to suppress the power consumption of the circuit forcontrolling the clamp. The clamp switch is usually turned on once for ablanking period.

However, in order to omit the switch 115 and the resistor 118 byshort-circuiting and opening them, respectively, it will suffice tocontrol the signal of the signal line 20R for switching the voltage ofthe voltage source 116. The clamp circuit functions as an asynchronouspeak clamp circuit in which the diode 112 and the transistor 113 isautomatically rendered conductive by increase in the video signal levelon the anode side of the diode 112 even if the voltage of the voltagesource 116 is not switched to be constant. Even if the voltage source116 is preset at a constant voltage, a high frequency component of thevideo signal leaked via the diode 112 by the influence of an absolutevalue of an inner impedance left in the voltage source 116 and a timeconstant may be detected by a diode 114 to cause a change in clamplevel. In this case, a minimum necessary capacitance to cancel thedetection action of the diode 114, for example a capacitor which is inthe order of several tens pF giving no adverse effect to the frequencyband range of the drive circuit is added to the diode 114 in paralleltherewith, or a Zener diode having a high parallel parastic capacitanceand the like may be used as the diode 114.

It is apparent that the coupling capacitor 111 which is charged with thedetected beam current 7R1 will not cause a problem such as sag in FIG.37 if it has a capacitance used for usual clamp circuits.

An embodiment in which the cathode current may be detected at theprestage of the compensation circuit if a bypass current other than thebeam current, or a leak current across the picture tube electrodes flowthrough the picture tube drive signal line is shown in FIG. 38. In orderto achieve a fast rise-up of the clamp operation after turning on of thepower source, a charging bias current may be caused to flow through thecoupling capacitor 111 via a resistor 34 or a series connection of theresistor 34 and the diode. However only beam current cannot be detectedsince the bias current is added without changing the prior art system.Accordingly, the bias current is cancelled by using a current controlledcurrent source 31 as shown in FIG. 38 so that it will not flow through adetection resistor 29. The current controlled current source 31 servesto detect the bias current 38 flowing through the input terminal 32thereof for supplying a current same as the detected bias current 38from an output current source 33. The current cancellation is madepossible by causing the output current to flow to the prestage of thedetection resistor 29 in the beam current path, for example, an outputpoint via at least one of output lines 25, 26 and 37 in the drawing. Thecathode current includes a leak current component from other electrodessuch as a heater 71R, a first grid, a second grid in addition to thebeam current component in the picture tube. However, the leak currentcomponent from the electrode separated among the primary colors R, G andB can be cancelled by connecting these electrodes with the prestige ofthe detection resistor 29 in the beam current path via resistors oractive elements. It is needless to say that the above mentionedoperation does not depend upon the type of picture tube drive electrode,such as cathode, each grid and anode.

A further embodiment for supplying a bias current to the levelcompensation circuit is shown in FIG. 39. In FIG. 39, the levelcompensation circuit comprises a current controlled voltage sourcecircuit using a transistor 1102. The voltage of the voltage sourcecircuit is controlled by a current flowing across input terminals 20R1and 20R2 of a photo coupler 20R0. A current controlled by a voltage of acontrol signal line 20R of FIG. 38 flows across both terminals 20R1 and20R2.

Although the inner impedance of the voltage source circuit will becomelower than that of a bypass capacitor 1101 for a high frequency signal,it depends the bias current, that is, it is substantially proportionalto the amount of the bias current of the transistor 1102 and becomes avalue which is not an infinetly zero. It is necessary to make thecontrol bias current constant or the sufficiently increase it incomparison with the beam current in order to suppress an adverse effectof the inner impedance on the voltage of the voltage source circuit.Therefore, a constant control bias current is caused to flow to thevoltage source circuit to drain a current equal to this bias currentfrom the prestage of a detection resistor 29 in the beam current pathfor making it possible to detect the beam current. The control biascurrent is determined by a temperature compensation diodes 323 and 321and a current flowing through the resistor 324 and flows from thetransistor to a transistor 331 via the regulated voltage circuit. Inthis case, a resistor 34 which is connected with the collector of thetransistor 322 serves to isolate a parastic capacitance on the side ofthe collector of the transistor 322 from a drive signal source forsuppressing the deterioration of the frequency characteristics of thedrive circuit. The collector of the transistor 331 is connected with atleast one of output lines 35, 36 and 37. A series resistor can beconnected with respective collectors of the transistors 322 and 331 andrespective transistors 321 and 322 to increase presetting precision ofthe control bias. It is also possible to thermally couple thetransistors 322 and 321 with the transistors 331 and 321, respectivelyor to form them on the same semiconductor chip, for example, an IC toenhance the thermal stability of the control bias current.

An embodiment in which a clamp circuit which is used as the levelcompensation circuit in the above embodiment is made applicable to awider band range picture tube drive circuit is shown in FIG. 40. In theembodiment of FIG. 40, the collector of a clamp transistor 113 isconnected with a drive signal source via a switch circuit 39 which isshort-circuited only on clamping operation. Since a collector and basecapacitance and a stray capacitance of the collector of the transistor113 will not be added to the drive signal source by providing the switchcircuit 39 for a display period during which a wide band range drivesignal is applied to a picture tube 6, further widening of the bandrange of the drive circuit would be possible. The voltage of a voltagesource 116 may be switching-controlled for a synchronous clamp circuitor alternatively may be constant for an asynchronous clamp circuit as issimilar to the case of FIG. 37. However, a diode is always connectedwith the drive signal source by provision of the clamp circuit so that acapacitance is added thereto. If it is necessary to reduce thecapacitance which is added via the diode 112, application of a reversevoltage upon the diode 112 for the display period makes it possible toin series connect another diode 1121 in the same polarity with the diode112.

A further embodiment of the switch circuit 39 shown in FIG. 40 is shownin FIG. 41. Since the collector current of the transistor 113 can beconsidered as zero, the anode voltage of a constant current diode 392will also become zero and a reverse voltage is applied to a diode 391 sothat the collector of the transistor 113 is isolated from the drivesignal source. However, the connection via the coupling capacitance ofthe diode 391 remains. Due to a fact that the collector current of thetransistor 113 becomes sufficiently larger than the current value of theconstant current diode 392 on clamping operation, the anode voltage ofthe constant current diode 392 will increase to render the diode 391conductive. Accordingly, most of the collector current will flow to acoupling capacitor 111 so that a stable clamping operation will becomepossible. Therefore, the diode 391 serves as an automatic switch. Notinga fact that the diode 391 is rendered conductive on clamping operationwhen the collector current of the transistor 113 increases, the constantcurrent diode 392 may be replaced with a resistor. The constant currentdiode 392 may also be replaced with a constant current circuit usingactive elements such as FETs. It is deemed that the switching speed ofthe diode 391 is inversely proportional to the parastic capacitance ofthe collector circuit of the transistor 113 and is governed by thethrough rate of the collector voltage proportional to the collectorcurrent of the transistor 113 on clamping operation. Therefore, it ispossible to connect with the cathode of the constant current diode 392an offset voltage source having a voltage which can be maintained insuch a range that the diode 391 is normally cut off on non-clampingoperation and that the coupling capacitance of the diode 391 will notcause a problem. For example, the cathode of the constant current diode392 is connected with a base bias voltage source terminal 242 of a basegrounded transistor 241 in a parallel relationship therewith.

An embodiment in which deterioration of the clamp accuracy is suppressedas much as possible is shown in FIG. 43.

By connecting a resistor 393 between the emitter of the transistor 241and the collector of the transistor 113, a current component flowingthrough a resistor 393 for switching a diode 391 can be returned to acoupling capacitor 111 again without flowing to the resistor 26 so thatthe claim accuracy is enhanced. That is, the emitter current (collectorcurrent) of the transistor 241 is decreased by an amount equal to thatof the current flowing to the resistor 393 and a current equal to thedecreased amount will flow to the coupling capacitor 111 from thecollector of the transistor 241. The resistor 391 can be designed sothat a resistance value in which a time constant of the collectorcircuit of the transistor 113 satisfies a necessary switching speed is amaximum value and a resistance value for enabling a current having suchan amount that the transistor 241 is not cut-off to flow is a minimumvalue. The resistor 393 may be replaced with a constant current diode,the anode of which is connected with the collector of the transistor 113as shown in FIG. 41. In this case, it is better to insert in series aresistor or an inductor for suppressing a high frequency signal leakedvia the constant current diode and a parallel parastic capacitance. Itis needless to say that same effect can be achieved even by connectingthe resistor 393 between the emitter of the transistor 24 and thecollector of the transistor 113.

A block diagram of a picture tube drive circuit 911 comprising a cathodecurrent detection and level compensation circuit 912 having both of alevel compensation capability and a beam current capability is shown inFIG. 44. The structure of FIG. 44 makes it possible to provide a highperformance such as reduction of circuit scale and enhancement ofreliability. The detailed structure of FIG. 44 is shown in FIG. 45. Itis possible to provide the level compensation circuit with a beamcurrent detection capability by commonly using a transistor in theclamping circuit to detect the beam current in the circuit in FIG. 45.

The switch circuit 115 is continued to be short-circuited for a beamcurrent detection period and is opened or closed for a clamp period ofthe other period for controlling a synchronous clamp operation. Theswitch circuit 40 is tilted to the side of the drive signal line onlyfor the clamp period for enabling a stable clamp operation.

A feature of the circuit shown in FIG. 45 resides in that a correctlevel compensation becomes possible without being influenced by thevideo signals since the voltage of the voltage source 116, the level ofwhich is controlled on beam current detection is transmitted to acathode 7R via a switch circuit 115 and the transistor 113 and the d.c.output of the video output circuit is cut off by a coupling capacitor111. Since the transistor 113 can be commonly used for clamping and beamcurrent detection, the circuit scale is reduced and the number ofportions which may be damaged by discharge in the picture tube and thelike is reduced, resulting in an enhancement of the reliability.

Since use of the switch circuit 40 can eliminate the addition of acapacitance to the drive signal source for a display period, furtherwidening of the band range of the drive circuit becomes possible a issimilar with the embodiment shown in FIG. 40. Also in the embodimentshown in FIG. 46, a constant current diode 402 is used to automaticallyrender a diode 401 conductive only for a clamping period when thecollector of the transistor 113 increases as is similar to theembodiment shown in FIG. 41. The clamping current will now be comparedwith the detection beam current flowing through the collector of thetransistor 113. The electric charge which has been stored in a couplingcapacitor 111 with a beam current flowing for a non-clamping period isabruptly discharged for a clamping period. Since the non-clamping periodis longer than ten times as the clamping period, it is deemed that theamount of the clamping current is not less than 10 times as much as thatof the detection current. Therefore, design of the constant currentdiode 402 is easy, and the constant current diode 402 may be replacedwith a resistor in some cases.

An embodiment in which the precision of the beam current detection canbe enhanced is shown in FIG. 47. The output of the video output circuitfrom the d.c. component to the a.c. component is completely cutoff froma cathode 7R by opening a switch circuit 41 only on detection of thebeam current in the embodiment of FIG. 47. Although a settling timeproportional to a time constant substantially determined by a product ofa coupling capacitor 111 and an output resistor 26 of the output circuitis required in order to detect the beam current when the switch circuit41 is normally short-circuited, the setting time can be neglected byopening the switch circuit 41.

The beam current can be detected while the output voltage of the videooutput circuit is applied to the cathode 7R by inserting a switchcircuit 42 in a path represented by a dot and chain line in FIG. 47, byshort-circuiting the switch circuit 42 only on detection of the beamcurrent and opening the switch circuit 41. Accordingly, it can beappropriately selected whether the voltage to be applied to the picturetube on detection of the beam current is supplied by a level controlledvoltage source 116 by opening a switch 42 to short-circuit a switchcircuit 115 or is supplied from the video output circuit byshort-circuiting the switch circuit 42 to open the switch circuit 115.

A further embodiment of the switch 41 shown in FIG. 47 is shown in FIG.48. In FIG. 48, a coupling capacitor comprises a capacitor for highfrequency signal and a capacitor for the other signals and the lattercapacitor may be cut-off from a drive signal source by a diode 411.Although the capacitor 119 in the drawing is an electrolytic capacitor,it may be any type of capacitor. The coupling capacitor 110 for highfrequency signal is made as low as possible in capacity so that thesettling time is negligible.

On turning on of power, a bias current will flow through capacitors 110and 119 via a bias resistor 413 from a power terminal 412 to commence anormal clamping operation. It is appropriate that the high frequencyimpedance of a diode 411 be inherently zero if it can be sufficientlyreduced. On detection of the beam current, a transistor is renderedconductive responsive to a signal from a detection signal source 416 tolower the collector voltage of the transistor so that the diode iscut-off. A resistor 417 is adapted to preset the base current of thetransistor 415. In order to carry out a fast control while saturatingthe transistor, a speed-up capacitor 419 and a base current drawingresistor 418 are added. A resistor 414 is inserted as shown in FIG. 48in order to prevent the base and collector capacitance of the transistor415 and the stray capacitance of a collector circuit from being added tothe drive line for a period when the beam current is not detected.Therefore, the resistor 414 functions as is similar to the resistor 291shown in FIG. 33.

A further embodiment which makes it possible to perform the beam currentdetection from a current of an electrode other than cathode electrode ofa picture tube is shown in FIG. 49. The outputs of a video outputcircuit 12 are applied to cathodes 7R, 7G and 7B of a picture tube 6 viaa level compensation circuit 11 in FIG. 29. Drive electrodes of thepicture tube 29 may be first grids if they are independent of with eachother for three primary colors R, G and B. In FIG. 49, a beam currentdetection circuit 9 is connected with an anode 6A to detect the beamcurrent which is a part of the anode current.

However, the beam detection circuit 9 may be connected with anyelectrode such as second and third grid, to which a current having acorrelation with the beam current flows. If the beam current of amulticolor picture tube excepting a monochrome picture tube is detectedfrom an electrode which is commonly used for a plurality of colors, thebeam current for each color should be separated by causing the beamcurrent for each color to flow at different timing. An embodiment of thedetailed circuit which is formed as mentioned above is shown in FIG. 50.In FIG. 50, the beam current detection circuit 9 comprises a rectifierdiode 600, a flyback transformer FBT601, voltage dividing resistorsR1602 and R2603 for stabilization of a high voltage by detecting thehigh voltage at a terminal 605, a resistor Rb604 for converting the beamcurrent into a voltage and a voltage source F_(R) for giving a d.c.shift to a beam current detection voltage. The beam current detectionvoltage is outputted to outside from a detection terminal 606. Thedetection voltage can be used as a beam current average value ABLcontrol voltage (automatic brightness limitation circuit controllingvoltage) by outputting the detection voltage from the ABL terminal 607via an integration circuit comprising a resistor R_(ABL) and a capacitorC_(ABL).

A current I_(FBT) of the flyback transformer which is to be detectedincludes an anode current I_(A) which is the beam current added With acurrent component leaked to each terminal of a picture tube 6, a currentI_(R) flowing through the voltage dividing resistors R1 602 and R2 603,distortion current components such as high order distortion current fora horizontal deflection period flowing across the ground and eachwinding of the flyback transformer. However, the beam current can beseparated and detected by detecting a change in a peak value, an averagevalue of the current I_(FBT) since the currents other than the beamcurrent have substantially constant amplitudes. Even if the amplitudesof the current components other than the beam current are notsufficiently low in comparison with the beam current, the average valuescan be deemed to be constant. Therefore, the beam current can easilydetected by using the above mentioned method.

An embodiment in which the present invention is applied to a dynamicload type video output circuit is shown in FIG. 51. In FIG. 51, thevideo output circuit uses a constant current source circuit and currentas a load of a video output transistor 24 to achieve reduction of powerconsumption. The video output circuit is added with a SEPP circuitcomprising transistors 43 and 45 as an output buffer for driving thepicture tube 6. Although the dynamic load circuit can achieve areduction of power consumption by suppressing the power source currentto a constant and low current irrespective of a high output voltage, itcannot supply an output current necessary to drive capacitive loads suchas a cathode 7R of a picture tube 6 with voltages of high amplitude andbroad band signals. Also in the output buffer SEPP circuit required forsuch a drive, drive of the picture tube 6 is made possible by operatingthe transistors in AB class in which an idling current which is high tosome extent flows across used transistor 43 and 45 for suppressing thecut-off level of the transistors at a low level. If the beam current isdetected by the dynamic load type video output circuit is used, theabove mentioned type detection circuit is disposed at the poststage ofthe video output circuit. Accordingly, an advantage of a low powerconsumption will be lost since the load capacity of the video outputcircuit is increased.

A feature of the present invention resides in that the beam currentdetection is achieved by a transistor 43 of the SEPP circuit as shown inFIG. 51. A terminal 48 is a power source terminal for biasing the SEPP.However, it is necessary to cut-off the idling current when the currentis detected. Accordingly, in accordance with the present invention, thecurrent of the constant current source or circuit 47 is controlled toreduce the current when the beam current is detected so that the biasvoltage of the SEPP circuit generated by the drop of the voltage acrossa biasing impedance 46 is controlled as shown in FIG. 51. By doing so,only the transistor 45 is cut-off when the beam current is detected. Inthis case, a diode 44 shown in FIG. 51 serves to stably cut-off thetransistor 45 also when the beam current to be detected is very low.This diode may be omitted (short circuited) when the detection currentis high to some extent, for example, less than 10 μA.

An embodiment which makes it possible to detect the beam current even ifthe dynamic load type video output circuit is used is shown in FIG. 52.In FIG. 52, a diode 44 is switch to brought into conductive andinconductive conditions by controlling the current of a constant currentcircuit comprising a transistor 471 for detecting the beam current.Diodes 462 and 463 which provide a biasing impedance perform atemperature drift compensation for an idling current. Accordingly, it ispossible to form transistors 43 and 45 on the same semiconductor deviceor to thermally couple them with each other. A bypass capacitor 464eliminates the directional property of the drive impedance of an SEPPcircuit. Resistors 431 and 451 are used for presetting the idlingcurrent and for protection of the transistors 43 and 65, respectively. Aresistor 452 is also used for protecting the transistor 45 from an overcurrent flowing on accidental contact. A capacitor 500 and a resistor501 form a bypass circuit for compensating the deterioration of thefrequency characteristics of the drive circuit due to the protectionresistor 284 and exhibits a high impedance for a discharge energy in thepicture tube 6. A transistor 471 which forms a constant current circuitconnects with a terminal 472 the a.c. component of the collector currentof the transistor 473 which is controlled by a current detection signalsource 416 and the collector current is received by a base groundedsystem biased by a resistor 474 and is supplied to an impedance forbiasing the SEPP circuit. The collector current of the transistor 473 isadjusted by a resistor 475. Fast control is made possible since thetransistors 473 and 471 are non-saturable. Although a parallel feedbackis applied to an output transistor 24 by an input resistor 490 and afeedback resistor 491, this feedback is maintained by cut-off of onlythe diode 44 also for a current detection period so that the outputvoltage of the transistor 43 is stably supplied to the picture tube 6.Since the base voltage of the transistor 471 is made constant also onswitching of the current detection, the leakage of the detection signalfrom a signal source 416 to the transistor 45 via a detection signalcapacitor 494 is suppressed. A negative feedback is also applied to thetransistor 471 by a resistor 495 and a capacitor 494. Each pair of aresistor 496 and a capacitor 497, and a resistor 492 and a capacitor 493is used for peaking. A Zener diode 253 is used for suppressing a fall ofthe operating point of the input signal source 31 caused by a d.c. biasof an input resistor 490 and a feedback resistor 491. A by-passcapacitor 254 reduces the impedance of the Zener diode 253 andcompensates for noise. The fall of the operating point is alsocompensated for by using a resistor 498. High output and wide band rangecharacteristics of the drive circuit can be maintained since there is nooutput capacity which is added for detecting the current in the presentembodiment.

A further embodiment which makes it possible to control the current ofthe constant current source or circuit is shown in FIG. 53. Currentcontrol is performed by controlling the base bias voltage of atransistor 471 which forms a constant current circuit in FIG. 5.Portions which are not illustrated are identical with those of theembodiment of FIG. 52. The current control is conducted by switching atransistor 51 to short-circuit a resistor 479. The base bias voltagewhen the resistor 479 is short-circuited is preset by a voltage across aterminal 476 and resistors 477 and 478. A resistor 512 is a baseresistor for presetting a base current of a transistor 51. If theswitching speed is enhanced, the value of the base resistor 512 isappropriately adjusted, or a speed-up capacitor 513 and a base currentdrain resistor 511 are used. The resistive voltage of the transistor 51can be made lower than that of the transistor 473 shown in FIG. 22.

It is needless to say that the picture tube may include plasma displaytube and the like as well as cathode ray tube, and accordingly the driveelectrode includes other electrodes other than cathode and grid. Thesemiconductors to be used may include a variety of active elements suchas GaAs FETs as well as bipolar transistors or diodes. The polarity ofthe elements may be reversed by reversing the polarity of potential.

We claim:
 1. A drive apparatus for a color picture tube, characterizedin that said apparatus comprises:a video output circuit which receivesvideo signals, amplifies said video signals and outputs the amplifiedvideo signals; a picture tube drive circuit which receives the amplifiedvideo signals from said video output circuit for driving the colorpicture tube based on said video signals, said picture tube drivecircuit having means for detecting a beam current corresponding to thebrightness of each color flowing through said picture tube; a picturetube connected with said picture tube drive circuit for displaying thevideo signals; a white balance control circuit into which a detectionvalue of a beam current detected by said picture tube drive circuit isinputted and for outputting level compensation video signals, foradjusting the white balance of the video image displayed on said picturetube, to said picture tube drive circuit; and a reference signal outputline from said white balance control circuit is connected with the inputof said video output circuit for inputting a white balance adjustingreference signal thereto and further including deflection control meanswhich is mounted on a deflection portion of said picture tube and iscontrolled by said white balance control circuit for controlling thedeflection of an electron beam of the picture tube to prevent said whitebalance reference signal from being displayed on a screen of saidpicture tube.
 2. A drive apparatus for a color picture tube as definedin claim 1 characterized in that said video signal level compensationsignal of said white balance control circuit to said picture tube drivecircuit is a cut-off control signal for inputting a relatively darkwhite signal as a white balance adjustment reference signal to adjustthe direct current level of said video input signal so that the ratio ofrespective beam currents of current red, green and blue colors become apredetermined ratio and in which said white balance control circuitreceives a relatively light white signal as the white balance adjustmentreference signal and outputs a drive adjustment signal for adjusting thegain of a drive adjustment means of said video input signal so that theratio of respective beam currents of current red, green and blue colorsbecome said predetermined ratio.
 3. A drive apparatus for a colorpicture tube as defined in claim 1 characterized in that said whitebalance control circuit comprises a timing signal generation circuit forgenerating a white balance adjustment timing signal from a verticalblanking signal and a horizontal blanking signal; a cut-off adjustmentcomparator which receives said cathode current detection value, comparesit with a given reference value for outputting a cut-off adjustmentsignal; a cut-off adjustment signal interruption means connected withthe output side of said cut-off adjustment comparator, which closesresponsive to the white balance timing adjustment timing signal fromsaid timing signal adjustment circuit for outputting said cut-offadjustment signal to said picture tube drive circuit; a cut-offadjustment hold capacitor connected with the output side of said cut-offadjustment signal interruption means; drive adjustment comparator whichreceives said cathode current detection value, compares it with a givenreference value and outputs a drive adjustment signal; drive adjustmentsignal interruption means connected with the output side of said driveadjustment comparator, which opens responsive to the white balancetiming adjustment timing signal from said timing signal generationcircuit for outputting said drive adjustment signal and a driveadjustment hold capacitor provided on the output side of the driveadjustment signal continuing means.
 4. A drive apparatus for a colorpicture tube as defined in claim 2 characterized in that said whitebalance control circuit includes a digital signal processing circuithaving a memory circuit and an operational processing circuit which ahorizontal blanking signal and a vertical blanking signal are inputtedinto and a given reference signal and a level adjustment/driveadjustment switching signal are outputted therefrom and comparing meansfor comparing an inputted cathode current detection signal with thereference value from said digital signal processing circuit foroutputting a result of the comparison, whereby said output signal isoutputted to said level adjustment means on level adjustment based onthe level adjustment/drive adjustment switching signal from said digitalsignal processing circuit and said output signal is outputted to saidlevel adjustment means on level adjustment and said output value isstored in the memory means in said digital signal processing circuit andsaid drive adjustment means outputs said output signal to said picturetube drive means and stores said output value in the memory means insaid digital signal processing circuit.
 5. A drive apparatus for a colorpicture tube as defined in claim 2 characterized in that said whitebalance control circuit comprises a digital signal processing circuitincluding an operational processing means having a memory circuit andfirst and second registers for receiving a horizontal and verticalblanking signals to output a given reference signal and a leveladjustment/drive adjustment switching signal, comparing means whichreceives said cathode current detection signal and compares it with areference value from said digital signal processing circuit foroutputting a result of the comparison; and an interface circuit forinputting the output of said comparing means to said operationalprocessing circuit, wherein said digital signal processing circuitinputs an intermediate value of a dynamic range for data into the firstregister and inputs a half of the value of the first register into thesecond register and subtracts the value of the second register from thefirst register if the output of said comparing means is negative andstores the result in the first register and adds the value of the firstregister to the value of the second register and stores the result inthe first register if the output of said comparing means is positive andrepeats (the number of control data bits minus 1) times the operation ofmaking the value of the second register a half of it to generate acontrol data.
 6. A drive apparatus for a color picture tube as definedin claim 1 characterized in that said picture tube drive circuitincludes a coupling capacitor for transmitting the video signalamplified by said video output circuit to the cathode side of thepicture tube; and a clamp circuit for periodically clamping the side ofsaid coupling capacitor coupled to said cathode side of said capacitorto a necessary level compensation voltage.
 7. A drive apparatus for acolor picture tube as defined in claim 1 characterized in that abrightness adjustment circuit which compares an inputted video signalwith a brightness control signal in a comparator which generates anerror signal and adds the error signal in an adder for performingbrightness adjustment at a poststage of said video output circuit and awhite balance adjustment reference signal is inputted to said picturetube drive circuit via said brightness adjustment circuit by inputtingthe reference signal for white balance adjustment to said comparator inlieu of said brightness control signal.
 8. A drive apparatus for a colorpicture tube as defined in claim 1 characterized in that said whitebalance control circuit is provided with a manual switch for initiatingan adjustment operation in said white balance control circuit.
 9. Adrive apparatus for a color picture tube as defined in claim 1characterized in that an input signal level detection circuit whichdetects any one of at least a peak value, a minimum value, and amomentary value at a given timing of each primary color signal of theinput video signals is provided at a prestige of said video outputcircuit and said white balance control circuit operates to control atleast any one of a peak value, a minimum value and a momentary value ata given timing of a beam current of each color inputted from saidpicture tube drive circuit based on the detected value inputted fromsaid level detection circuit.
 10. A drive apparatus for a color picturetube as defined in claim 1 characterized in that an optical sensor whichcan detect the display screen of said picture tube and said whitebalance control circuit outputs said video signal level compensationsignal for performing white balance adjustment based on adjustment datafor drive and cut-off adjustment in a preliminarily stored beam scanningposition.
 11. A drive apparatus for a picture tube as defined in claim 1characterized in that means for detecting the beam current of saidpicture tube drive circuit is formed to detect the beam current flowingin said color picture tube from change in a current flowing through aflyback transformer coil connected with an anode terminal of saidpicture tube.
 12. A drive apparatus for a color picture tube as definein claim 1 characterized in that said white balance control circuitstores compensation data of the beam current of the picture tube forwhite reference and compensating for brightness and chromaticityirregularities and their changes with age on the picture tube screen andgenerates said beam current level compensation signal for compensatingfor said brightness and chromaticity irregularities in accordance withthe lapse of time based on the stored data.
 13. A drive apparatus for acolor picture tube as defined in claim 12 characterized in that saidpicture tube is a projection type picture tube and said optical sensoris disposed on the projection side of the screen.
 14. A drive apparatusfor a color picture tube as defined in claim 1 characterized in thatsaid white balance control circuit outputs a beam current compensationreference voltage and a white balance adjustment reference signal andcolor temperature control of a white reference is made possible bymaking variable the beam current compensation reference voltage and thewhite balance adjustment reference signal level outputted from saidwhite balance control circuit.
 15. A drive apparatus for a color picturetube as defined in claim 1 characterized in that color temperaturecontrol of white reference is made possible by making variable a beamcurrent detection resistor in the picture tube drive circuit for atleast one color of primary colors.
 16. A drive apparatus according toclaim 15, wherein two colors of the primary colors are adjusted.